fix functions --copy

Fixes #3601

src/builtin.cpp

@@ -1194,7 +1194,7 @@ static int builtin_functions(parser_t &parser, io_streams_t &streams, wchar_t **
             return STATUS_BUILTIN_ERROR;
         }
 
-        if ((wcsfuncname(new_func) != 0) || parser_keywords_is_reserved(new_func)) {
+        if (!wcsfuncname(new_func) || parser_keywords_is_reserved(new_func)) {
             streams.err.append_format(_(L"%ls: Illegal function name '%ls'\n"), argv[0],
                                       new_func.c_str());
             builtin_print_help(parser, streams, argv[0], streams.err);

tests/function.in

@@ -35,12 +35,26 @@ frob
 # `name4` were created. See issue #2068. That behavior is not what we want.
 # The function name must always be the first argument of the `function`
 # command. See issue #2827.
-function name1 -a arg1 arg2 ; end
+function name1 -a arg1 arg2 ; echo hello; end
 function -a arg1 arg2 name2 ; end
-function name3 --argument-names arg1 arg2 ; end
+function name3 --argument-names arg1 arg2 ; echo hello; echo goodbye; end
 function --argument-names arg1 arg2 name4 ; end
 function name5 abc --argument-names def ; end
 functions -q name1; and echo "Function name1 found"
 functions -q name2; or echo "Function name2 not found as expected"
 functions -q name3; and echo "Function name3 found"
 functions -q name4; or echo "Function name4 not found as expected"
+
+# Verify that functions can be copied. Tests against regression of issue #3601.
+functions -c name1 name1a
+functions --copy name3 name3a
+functions -q name1a
+or echo "Function name1a not found as expected"
+functions -q name3a
+or echo "Function name3a not found as expected"
+echo Checking that the copied functions are identical other than the name
+diff (functions name1 | psub) (functions name1a | psub)
+diff (functions name3 | psub) (functions name3a | psub)
+# The diff would cause us to exit with a non-zero status even if it produces
+# the expected output.
+exit 0

tests/function.out

@@ -22,3 +22,12 @@ Function name1 found
 Function name2 not found as expected
 Function name3 found
 Function name4 not found as expected
+Checking that the copied functions are identical other than the name
+1c1
+< function name1 --argument arg1 arg2
+---
+> function name1a --argument arg1 arg2
+1c1
+< function name3 --argument arg1 arg2
+---
+> function name3a --argument arg1 arg2